Next generation wireless systems make use of multiple transmitters and receivers (i.e., multiple antenna systems) in a mobile device and in a base station. Multiple antenna systems are also known as Multiple Input, Multiple Output (MIMO) systems. The availability of multiple transmitters and receivers provides for communicating data over multiple paths or streams in the uplink and downlink directions. For example, in a MIMO system, spatial diversity can be used to make data transmission more robust or reliable. More specifically, using spatial diversity, robustness or reliability is increased by transmitting the same data redundantly over the same channel using multiple antennas. In other words, the transmitting device creates multiple data streams of the same data and transmits the multiple streams over the same channel using different antennas.
Consequently, a recipient device (also referred to herein simply as a recipient) receives two or more copies of the same data. Because the recipient has two or more copies of the data, the recipient can correct errors that occurred in the original transmission without requesting a data retransmission, thereby increasing robustness. However, robustness comes at a cost of increased battery consumption when implementing spatial diversity since multiple transmitters are used to drive multiple antennas. Thus, if at all possible, transmissions using spatial diversity should be selectively performed.
Accordingly, there is a need for methods and apparatus for selectively transmitting data using spatial diversity.
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The apparatus and method components have been represented where appropriate by conventional symbols in the drawings, showing only those specific details that are pertinent to understanding the embodiments of the present invention so as not to obscure the disclosure with details that will be readily apparent to those of ordinary skill in the art having the benefit of the description herein.